Nozzle configurations for abrasive blasting

ABSTRACT

Disclosed herein are nozzle configurations for an abrasive blasting system. The system can comprise multiple hoppers for feeding separate powders streams to a fluid jet. The separate powder streams can be mixed in a frustoconical or conical mixer prior to delivery to the substrate surface. Also disclosed are methods of texturizing the substrate surface by moving the substrate or nozzle(s) during the delivery of dopant(s). Methods for achieving a uniform distribution of dopant are also described. Also disclosed herein are coaxial nozzle configurations having an outer focusing stream to converge and/or mix with an inner particle stream.

RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119(e) to U.S. Prov. App. 61/035,985, filed Mar. 12, 2008, U.S. Prov. App. 61/035,982, filed Mar. 12, 2008, and U.S. Prov. App. 61/038,200, filed Mar. 20, 2008, the disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods of coating and/or impregnating and/or otherwise modifying surfaces with dopants via abrasive blasting.

BACKGROUND OF THE INVENTION

The bombardment of metal surfaces with abrasive materials is finding an increasing number of technical applications in recent years. Techniques such as grit blasting, shot blasting, sand blasting, shot peening and micro abrasion fall under this category of surface treatment technique. In each of these techniques, generally, an abrasive material, shot or grit, is mixed with a fluid and delivered at high velocity to impinge the surface to be treated. The technique used to deliver the abrasive material can be classified as wet or dry depending on the choice of fluid medium used to deliver the abrasive to the surface, usually water and air respectively.

Applications of these technologies include metal cutting, cold working metallic surfaces to induce desirable strain characteristics and the pre-treatment of surfaces to induce desirable texture (surface roughness) for the purposes of enhanced adhesion of further coating materials. (See Solomon et al., Welding research, 2003. October: p. 278-287; Momber et al., Tribology International, 2002. 35: p. 271-281; Arola et al., J. Biomed. Mat. Res., 2000. 53(5): p. 536-546; and Arola and Hall, Machining science and technology, 2004. 8(2): p. 171-192.).

Abrasive blasting finds various applications industries, such as the automotive, aerospace, construction, medical, and other industries that involve surface texturing or smoothing. Due to the variety of surfaces involved, including different material types, textures, hardness, etc., a need remains for new nozzle configurations for abrasive blasting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an abrasive blasting system having multiple hoppers for separate particle feeds that converge via a mixer;

FIG. 1B shows a mixer for separate particle streams;

FIG. 2A shows a frustoconical block mixer having inner channels;

FIG. 2B shows another a frustoconical block mixer where the channels have a different incident angle from those of FIG. 2A;

FIG. 3A shows a two-nozzle configuration where each nozzle has an incident angle of 45°;

FIG. 3B schematically depicts the “interaction zone overlap” (IZO) of the configuration of FIG. 3A.

FIG. 3C shows a two-nozzle configuration in which the incident angle is 5°;

FIG. 3D schematically depicts the “interaction zone overlap” (IZO) of the configuration of FIG. 3C;

FIG. 4A schematically depicts a dopant track deposited when the substrate is moved horizontally;

FIG. 4B schematically depicts a dopant track deposited when the substrate is moved horizontally in a direction opposite that of FIG. 4A;

FIG. 4C schematically depicts two different dopant tracks deposited on a single substrate when the substrate is moved in two opposing directions;

FIG. 4D schematically depicts a dopant track comprising a series of linear tracks;

FIG. 4E schematically depicts a dopant track comprising a circular pattern;

FIG. 5A shows a cross-section of the width of a dopant track that is non-uniformly distributed (weighted toward the middle);

FIG. 5B shows the Guassian distribution of the powder density (y-axis) versus diameter of powder stream (x-axis) based on the dopant track cross-section of FIG. 5A;

FIG. 5C shows a cross-section of the powder stream, showing the non-uniform distribution of powder that results in the dopant track of FIG. 5A;

FIG. 5D shows a cross-section of the width of a dopant track that is uniformly distributed;

FIG. 5E shows a “top hat” distribution of the powder density (y-axis) versus diameter of powder stream (x-axis) based on the dopant track cross-section of FIG. 5D;

FIG. 5F shows a cross-section of the powder stream, showing the uniform distribution of powder that results in the dopant track of FIG. 5D;

FIG. 6A shows the extent of overlap (“O”) of dopant tracks required for a uniform surface coating based on the non-uniform dopant track of FIG. 5A;

FIG. 6B shows the smaller extent of overlap (“O”) of dopant tracks required for a uniform surface coating based on the uniform dopant track of FIG. 5D;

FIG. 7 shows a coaxial nozzle configuration having an outer, focusing stream;

FIG. 8A shows a block mixer having a multiple nozzle configuration with four side feed nozzles;

FIG. 8B schematically depicts the particle stream emanating from the nozzle configuration of FIG. 8A;

FIG. 9A shows the mass flow rates of abrasive versus dopant for increasing amounts of A to D;

FIG. 9B is an expanded area of interest of FIG. 9A, for finer control of the dopent concentration; and

FIG. 10 shows a block mixer having a Y-shaped channel configuration.

DETAILED DESCRIPTION

Disclosed herein are systems and treatment processes for impregnating a surface, such as a metal surface, with a dopant. The strength of the bond between the dopant and the surface and the concentration of dopant achieved in or on the surface can be improved over conventional methods of surface impregnation techniques.

Abrasive blasting is typically used for cleaning or stripping substrates of an outer surface. The present invention employs the abrasive blasting technique to not only clean the outer surface but to modify the surface with a dopant.

If a dopant material is delivered to the surface within a high velocity fluid jet in the absence of an abrasive, no or minimal surface modification will occur. Such circumstances can arise for a number of reasons; the material may not have sufficient particle size, or have sufficient density and hardness. It may also be a consequence of the nature of the surface itself. For metal surfaces, for example, the dopant material would require suitable physical properties (e.g., density and/or hardness) to breech an oxide layer to access the underlying metal surface.

One embodiment provides an apparatus for abrasively blasting a substrate, comprising:

at least two hoppers for receiving at least two sets of particles including a first set of particles comprising an abrasive and a second set of particles comprising a dopant;

a mixer for receiving and mixing the at least two sets of particles from the at least two hoppers to form a particulate mixture; and

at least one fluid jet for delivering the at least two sets of particles to the mixer, or the particulate mixture to the substrate, the at least one fluid jet being positioned downstream of the at least two hoppers.

In one embodiment, the at least one fluid jet is positioned at the base of the at least two hoppers. In another embodiment, the at least one fluid jet is positioned at the base of the mixer.

FIG. 1A shows one embodiment of a system 2 containing at least two hoppers for delivering particulate material to a fluid jet used for abrasively blasting a substrate. The apparatus of FIG. 1A contains multiple hoppers 4 (labeled hoppers 1, 2, 3 . . . n), where each hopper 4 delivers a powder through individual delivery tubes 5 leading to a common mixer. At least one of the hoppers delivers an abrasive (A), such as Al₂O₃, for abrasively blasting a surface of the substrate. For example, the substrate can be a metal and the alumina can be used to abrasively blast the oxide surface to expose the underlying metal surface. One embodiment takes advantage of the removal of the oxide layer overlying the metal substrate, and treating the newly exposed metal beneath to add a new material (the dopant). Depending on the nature of that added material, the surface properties of the metal article can be tailored according to its intended functional requirements.

At least one of the hoppers delivers the dopant that is deposited on the metal surface underlying the metal oxide layer. In the embodiment of FIG. 1A, at least two dopants can be deposited on the metal surface, each dopant being delivered from individual hoppers to the mixer. For example, hopper 1 can receive and deliver the abrasive (A), hopper 2 can deliver a first dopant D1 (e.g., hydroxyapatite), and hopper three can deliver a second dopant D2 (e.g., a drug). It is readily appreciated that one or more dopants may be delivered in combination with one or more abrasives, and one of ordinary skill in the art can readily envision constructing arranging multiple (n) hoppers to handle as many dopant/abrasive types as needed.

Each powder type is delivered from the respective hopper to a common mixer 8 where the particles can be mixed to form a more homogeneous particulate mixture comprising the abrasive and dopant(s). From the mixer 8, a powder stream of the abrasive and one or more dopants is delivered to an interaction zone 10 (e.g., a substrate surface).

To achieve abrasive blasting of the pressurized surface, a fluid jet (not shown) delivers at least the abrasive (A) to and from the mixer 8 to produce an accelerated powder stream that bombards the substrate surface (enters interaction zone 10). The fluid jet can deliver the powder stream via a pressurized fluid, which can be a liquid or gas. In another embodiment, a fluid jet also delivers the one or more dopants. The fluid jet(s) can be positioned at the base of respective hoppers to accelerate particles through the tubing 5 and to the mixer 8. The velocity of the particles can enhance the mixing and the particles have sufficient velocity to bombard the substrate surface and impregnate it with dopant. In another embodiment, the fluid jet can be positioned at the base of the mixer to accelerate particles from the mixer to the substrate surface.

FIG. 1A shows the mixer having a conical shape, although a frustoconical shape can be also applied. Various mixer shapes can be envisioned so long as the shape allows the mixer to receive multiple powder streams and to aggregate these streams into a more homogeneous particulate mixture. FIG. 1B shows a detailed view of mixer 18 comprising a feed section 22 leading to a cylindrical section 24 that converges downwardly (toward the interaction zone 20) to a conical or frustoconical section 26. The feed section 22 contains apertures for the delivery tubes 18, allowing entry of the abrasive (A) and dopant(s). After entry of the powders into the mixer 18, the configuration of mixer 18 allows powder streams to impact the side walls of the cylindrical section 22 and mix throughout its length, potentially allowing greater mixing of the powders. The embodiment of FIG. 1B also demonstrates the varying angles from which the abrasive and dopant stream(s) can enter the mixer 18 at feed section 22. The configuration of delivery tubes 15 in FIG. 1B has the abrasive powder stream pointed at an angle 90° from the vertical toward the mixer. This abrasive stream will collide in the mixer 18 with the dopant stream, which can enter the mixer 18 at an angle at 0° from the vertical (e.g., dopant 1) or at another angle ranging between 0° and 90° (e.g., as with dopant 2). Upon collision with the abrasive powder stream, the mixed powder stream can swirl in the direction of arrow 28, allowing greater mixing of the powders. This mixer design can provide increased and more efficient mixing. In one embodiment, at least one abrasive stream is delivered with a pressurized fluid such that the abrasive hits the dopant streams with sufficient force to cause impregnation of the dopant on the abrasive before the particles hit the substrate surface.

In one embodiment, the mixer is a funnel or funnel-like structure, as in FIG. 1A. In another embodiment, the mixer can be open at the top or can have a closed structure save for inlet holes at the top for attaching tubing connecting the mixer to the hoppers. One exit hole can be positioned at the bottom of the mixer; alternatively, more than one exit hole can be provided, resulting in a two, three, or multi-pronged junction where the different particle streams meet at a point below the mixer. For example, alumina can serve as the abrasive and hydroxyapatite can serve as the dopant, where both sets of particles are fed to and mixed in the mixer, allowing the particles to be delivered to the interaction zone or substrate substantially simultaneously.

In one embodiment, the hopper contains a nozzle (fluid jet) at its base and a source of pressurized fluid to emit a particle stream to the mixer at high speed. In one embodiment, only the abrasive is delivered to the mixer at high speed. One or more dopants may or may not be delivered to the mixer at high speed. By adjusting the respective flow rates of the abrasive and dopant(s), the ratio of abrasive to dopant(s) can effectively be adjusted and controlled while maintaining a constant overall mass flow rate.

Another embodiment provides an apparatus for abrasively blasting a substrate, comprising:

a first particle stream comprising an abrasive and a second particle stream comprising a dopant;

a conical or frustoconical mixer comprising at least two channels penetrating through the mixer, wherein the respective particle streams enter the channels separately and exit the mixer to impact the substrate as a particulate mixture of the first and second particle streams; and

at least one fluid jet to deliver at least one of the first and second particle streams to the mixer, or to deliver the particulate mixture to the substrate.

In one embodiment, the at least one fluid jet is positioned upstream of the mixer to deliver at least one of the first and second particle streams to the mixer. In another embodiment, the at least one fluid jet is positioned between the mixer and the substrate to deliver the particulate mixture to the substrate.

Another embodiment provides an apparatus for abrasively blasting a substrate, comprising:

a first fluid jet for delivering a first particle stream comprising an abrasive and a second fluid jet for delivering a second particle stream comprising a dopant to be impregnated in the substrate; and

a solid conical or frustoconical block positioned between the fluid jets and the substrate or upstream of the fluid jets;

channels penetrating through the length of the block for separate particle streams,

wherein the particle streams enter the channels from a top surface of the block and exit from the bottom of the block before impacting the substrate.

FIG. 2A shows one example of a mixer configured as a solid block 30. Block 30 has a funnel shape where at its greatest width (top of funnel), the block has a flat top surface 32. From the top surface 32 the shape of the block converges to its smallest width 34 at the bottom. Block 30 has three channels 36 drilled from the top surface 32 through the bottom 34 to allow a powder stream to travel through the block. Optionally, a feed nozzle 33 stemming from the channels 36 can provide an entry way for the respective powders into block 30. Feed nozzle 33, although shown as a tube, can alternatively be funnel-shaped, cup-shaped, or any other shape known in the art to enhance optimal delivery of powder to block 30. At a fixed distance “d1” from the bottom, the respective powder streams reach a focal point at 38 prior to hitting the substrate surface (not shown). Thus, block 30 comprises channels initiating from the top (planar) surface of the conical or frustoconical mixer and penetrating substantially the length of the mixer. As depicted in FIG. 2A, the mixing occurs after the separate particle streams have exited the mixer but before impacting the substrate

The distance “d1” can be varied depending on the incident angle of the channels (with respect to the vertical), as in FIG. 2B. FIG. 2B shows a block 40 of a similar funnel shape to block 30 of FIG. 2A. Block 40 has a different incident angle of the channels 46 with respect to the longitudinal axis of the block, resulting in the distance “d2” between the bottom 44 and focal point 48 being greater than that of d1. In one embodiment, for a conical or frustoconical block having a longitudinal dimension of about 50 mm (the distance between the top surface and the bottom), the distance between the exit point of the mixer and the focal point (“d1” or “d2”) can range from 10-20 mm, e.g., from 10-15 mm.

The blocks of FIGS. 2A and 2B can be used for fixed incident angles in the situation where incident angles have been optimized and their variation is not necessary. Blocks 30 and 40 provide a more robust construction for delivery of multiple powder streams. The nozzle block can be made from copper or tool steel. Two or more channels can be readily envisioned, as demonstrated in FIGS. 2A and 2B.

FIG. 8A shows a block 50 having a multiple nozzle configuration in which four side feed nozzles 53 a (only two shown) surround a central nozzle 53 b positioned at top surface 52. In FIG. 8A, the central feed nozzle 53 b delivers the abrasive A and the four side feed nozzles 53 a deliver one or more dopants (D1-D4), which can be the same for each nozzle or different. The side feed nozzles 53 a are illustrated as delivering powder to channels 56 at 90° radially relative to each other. With this arrangement, the dopant powder can exit the bottom 54 and simultaneously arrive at the focal point 58 of the powder stream along with the abrasive. Multiple nozzles can improve the uniformity of the deposited layer by impregnating the dopant from all angles.

FIG. 8B depicts a schematic side view of two of the dopant powder streams 62 a and 62 b and abrasive stream “A” impinging substrate 64. The entire nozzle arrangement can move in a direction normal to the vertical as indicated by double arrow 66 (i.e., horizontally, or parallel to the substrate surface) while the substrate 64 remains stationary. Alternatively, the substrate 64 can move horizontally (in a direction parallel to the substrate surface) in the direction of double arrow 68 while the nozzle configuration remains stationary. The movement of the substrate/nozzles can affect the amount of dopant incorporation in the substrate. For example, if the substrate 64 moves to the right in FIG. 8B, then the dopant from powder stream 62 b will be lightly impregnated in the substrate due to some stripping from the trailing abrasive stream A. Meanwhile, dopant emanating from powder stream 62 a may be incorporated in the substrate to a greater extent.

In another embodiment, the block 50 of FIG. 8A can be configured to deliver the dopants in an annular ring 57 surrounding the central channel that delivers the abrasive stream. In one embodiment, the annular ring is formed from a circular feed nozzle (not shown). In another embodiment, the annular ring is formed from multiple nozzles arranged in a circle surrounding the central nozzle. Depending on the motion of the substrate or nozzle apparatus, the amount of dopant delivered to the substrate can be controlled.

The nozzle configurations of FIGS. 8A and 8B can deposit dopant in gradients or in layers depending on the choice of dopant, the position of the dopant stream with respect to the central nozzle, the mass flow rate of dopant and abrasive, the velocity of movement of the nozzle or substrate, etc. It will be readily appreciated by one skilled in the art that any number of dopant streams can be incorporated, as limited by the size of the block 50, the channels 56, etc.

Another embodiment of a block is depicted in FIG. 10. Block 200 comprises a conical shaped device with two openings 202 on the top into which the dopant and abrasive are fed. More than two openings can be constructed. Openings 202 lead to channels 204, which merge to a single channel 206 around the center of the block 200. This Y-shaped pathway allows the powders to mix before they exit through a single opening 208 at the bottom of the device.

FIG. 3A shows a two-nozzle configuration where both nozzles 72 a and 72 b are spaced a distance apart, and each nozzle having an incident angle 74 from the normal (or angle of inclination) of 45°. The two respective streams 76 a and 76 b first meet and interact at a volume 78 above the substrate 80. An expanded view of volume 78 is shown in FIG. 3B, and is also termed the “interaction zone overlap” (IZO).

FIG. 3C illustrates another dual nozzle configuration in which the nozzles 82 a and 82 b are maintained at the same distance from the substrate as the nozzles in FIG. 3A but the incident angle 84 is changed to 5°. The volume 88 for the nozzle configuration of FIG. 3C is illustrated in FIG. 3D. It can be seen that the IZO based on the volume 88 as shown in FIG. 3D (smaller incident angle) is greater than the IZO of volume 78 of FIG. 3B, as the base of the volumes are the same, but the height of the volume 88 increases as the incident angle 84 decreases.

A larger IZO provides a longer time period for the two powder streams to interact with each other before hitting the substrate, and thus, the efficiency of mixing is greater for an embodiment such as FIGS. 3C and 3D, compared with the embodiment of FIGS. 3A and 3B. In other embodiments, a shorter interaction time period may be desired.

Another embodiment provides a method of modifying a substrate, comprising:

delivering substantially simultaneously a first set of particles comprising a dopant and a second set of particles comprising an abrasive from at least one fluid jet to a surface of the substrate to impregnate the substrate with the dopant, each nozzle having an incident angle to the vertical ranging from 0° to 85°; and

moving the substrate in at least one horizontal direction during the delivering to deposit a track of the dopant on the substrate surface.

One embodiment of this method is demonstrated in FIG. 4A, showing the abrasive (A) and dopant (D) (e.g., HA) particle streams emanating from a two-nozzle configuration. In this embodiment, the substrate 100 (e.g., a Ti coupon), is moved in a horizontal direction (normal to the vertical) in the direction of arrow 102 (to the left) to create a track 104 of the deposited dopant. FIG. 4B shows the same particle streams and resulting patterns but for the situation where the substrate 100 is moved horizontally in the direction of arrow 108 (to the right), resulting in deposited track 106.

FIG. 4C shows the two line patterns 104 and 106 of deposited dopant on the same substrate 100. It was unexpectedly discovered that without changing the stream of abrasive and dopant, the track texture differed depending on the direction of traverse of the substrate, manifesting in a visual difference of the two substrate surfaces. In one embodiment, the color of the Ti coupon layer can vary depending on the direction of traverse of the substrate.

In one embodiment, the substrate is moved in more than one horizontal direction. In this embodiment, the dopant can be deposited on the substrate 110 in a pattern, as illustrated in FIGS. 4D and 4E. FIG. 4D shows a continuous pattern 112 of linear tracks where the direction of travel (see arrows 114) was changed 90° from the previous direction. FIG. 4C shows a circular direction of travel, resulting in a circular pattern 116.

Although FIG. 4D depicts a pattern created by twin nozzles, each delivering a set of particles (abrasive “A” and dopant “D” respectively), and FIG. 4E depicts a pattern created by either coaxial nozzles or a single nozzle feeding both the abrasive “A” and dopant “D,” it would be readily understood by one skilled in the art that the nozzle configurations can be reversed for FIGS. 4D and 4E. For example, the pattern of FIG. 4D can be delivered by a single nozzle or coaxial nozzles, while the circular pattern of FIG. 4E can be delivered by twin nozzles having the same or unique incident angles.

Another embodiment provides a method of controlling the distribution of a track deposited by one or more particle streams comprising an abrasive and dopant(s). FIG. 5A depicts a cross-section of a deposited dopant track 122 on substrate 120. It can be seen that the cross-section of track width 122 can have a nonhomogeneous distribution, where a greater proportion of the dopant is deposited in the middle of the track. The result is a Gaussian distribution of dopant when plotting powder density (y-axis) versus diameter of powder stream, as depicted in FIG. 5B. FIG. 5C shows a cross-section of the dopant powder stream emanating from the nozzle, indicating a greater dopant concentration in the center of the particle stream cross-section, thereby producing the nonhomogeneous deposit of FIG. 5A.

The effect of a nonhomogeneous distribution can be seen in a layer formed from multiple overlapping parallel tracks. If each track displayed a Gaussian distribution, a layer of uniform thickness can be achieved but only with a large overlap between adjacent, parallel tracks. In some instances, a nonhomogeneous distribution may require an overlap (“O”) between adjacent tracks of about 70%, as schematically illustrated in FIG. 6A.

Accordingly, another embodiment provides a method of improving the homogeneity of the distribution of a deposited track. In one embodiment, a method of modifying a substrate, comprises:

delivering substantially simultaneously a first set of particles comprising a dopant and a second set of particles comprising an abrasive from at least one fluid jet to the substrate to impregnate the substrate with the dopant,

wherein the first and second set of particles overlap at an area between the at least one fluid jet and the substrate, and

wherein a cross section of the overlap area has a substantially homogeneous distribution of the first set of particles.

FIG. 5D schematically depicts a cross-section of a deposited track 124 on substrate 120. A plot of powder density (y-axis) versus φ of powder stream would result in a uniform “top hat” distribution, as schematically depicted in FIG. 5E. The resulting cross-section of the powder stream would also be uniform, as depicted in FIG. 5F. For a uniform distribution, the overlap (“O”) of adjacent tracks can be as low as 5-10% to result in uniform surface coverage and thickness, as schematically illustrated in FIG. 6B.

In one embodiment, a particle stream cross-section having a uniform distribution of dopant(s) can be achieved with an apparatus for abrasively blasting a substrate, comprising:

a coaxial nozzle for delivering a stream of particles,

wherein an inner tubing of the nozzle delivers a first particle stream, and an outer tubing delivers a focusing stream that encircles and converges inwardly toward the first particle stream, and

wherein the stream of particles comprising the first particle stream bombard and impregnate and/or coat the substrate with the dopant.

FIG. 7 shows an embodiment of a coaxial nozzle 150, in which a particle stream is emitted through an inner tubing 152 of the nozzle 150. A focusing stream (F) can be delivered through an outer coaxial tubing of the nozzle, resulting in the emission of a the particle stream surrounded by the focusing stream.

In one embodiment, the inner tubing 152 delivers a first particle stream comprising an abrasive and dopant (e.g., alumina and hydroxyapatite), resulting in an emission of the two particle types as a single particle stream. In one embodiment, the focusing stream F is a pressurized gas delivered through an outer coaxial tubing of the nozzle, resulting in the emission of a single particle stream comprising abrasive and dopant surrounded by the pressurized gas. The pressurized gas can cause the particles to converge inwardly, resulting in additional mixing or homogenizing of the two particle types. The resulting mixture can then bombard and impregnate the surface of the dopant; because of the improved mixing efficiency, a more uniform distribution of deposited dopant can result.

FIG. 7 shows the particle stream entering the coaxial nozzle in a direction parallel to the longitudinal axis of the nozzle whereas the pressurized gas has an inlet normal to the longitudinal axis. One of ordinary skill in the art can readily appreciate that varying inlet angles for the gas or particles can be constructed as alternative designs for the nozzle.

Another embodiment provides an apparatus for abrasively blasting a substrate, comprising:

a coaxial nozzle for delivering a first set of particles comprising at least one dopant and a second set of particles comprising an abrasive,

wherein an inner tubing of the nozzle delivers a particle stream comprising a first set of particles, and an outer tubing delivers a pressurized gas comprising the second set of particles that encircles and converges inwardly toward the first set of particles to mix and homogenize the first and second set of particles, and

wherein a resulting mixture of the first and second particles bombard and impregnate and/or coat the substrate with the at least one dopant.

In one embodiment, a particle stream cross-section having a uniform distribution of dopant(s) can be achieved with an apparatus for abrasively blasting a substrate, comprising:

a coaxial nozzle for delivering a first set of particles comprising at least one dopant and a second set of particles comprising an abrasive,

wherein an inner tubing of the nozzle delivers a particle stream comprising a mixture of the first and second set of particles, and an outer tubing delivers a pressurized gas that encircles and converges inwardly toward the particle stream to mix and homogenize the first and second set of particles, and

wherein a resulting mixture of the first and second particles bombard and impregnate and/or coat the substrate with the dopant.

Another embodiment provides a method of controlling the flow rates of a particle mixture. By mixing the ratio of flow rates of abrasive (A) to dopant (D) a map of dopant concentrations over a range of flow rates can be created. FIG. 9A shows the mass flow rates of A versus D for increasing amounts of A to D. By choosing a range of mass flow rates from minimum (zero mass flow rate) to maximum (determined by the powder feeder specifications) one can impregnate a range concentrations of dopant into a surface. If an area of interest was determined from analysis of this map then that area of interest can be expanded and finer control of the dopant concentration can be obtained, as depicted in FIG. 9B.

In certain embodiments, the dopant materials include but are not limited to materials desired at an implant surface for the purposes of steering and improving the body tissue-implant interaction. The dopant can comprise materials such as polymers, metals, ceramics (e.g., metal oxides, metal nitrides), and combinations thereof, e.g., blends of two or more thereof.

Exemplary dopants include, modified calcium phosphates, including Ca₅(PO₄)₃OH, CaHPO₄.2H₂O, CaHPO₄, Ca₈H₂(PO₄)₆.5H₂O, α-Ca₃(PO₄)₂, β-Ca₃(PO₄)₂ or any modified calcium phosphate containing carbonate, chloride, fluoride, silicate or aluminate anions, protons, potassium, sodium, magnesium, barium or strontium cations.

Other exemplary dopants include titania (TiO₂), zirconia, hydroxyapatite, silica, carbon, and chitosan/chitin.

In one embodiment, the dopant is a combination of an agent-carrying media and at least one therapeutic agent (including biomolecules and biologics). Potential carriers for therapeutic agents including antibiotics, immuno suppressants, antigenic peptides, bactericidal peptides, structural and functional proteins have been disclosed in U.S. Pat. No. 6,702,850). Calcium phosphate coatings as the drug carrier can also be used (see U.S. Pat. Nos. 6,426,114, 6,730,324, and U.S. Provisional Application No. 60/410,307, the disclosures of which are incorporated herein by reference). Dopants that can act as agent-carrying media include nanoporous, mesoporous, nanotubes, micro-particles of various materials including hydroxyapatite, silica, carbon, and titania (TiO₂) capable of carrying therapeutic agents, biomolecules and biologics. Particulates and powders (e.g. titania powder) can be either adhesively bonded or covalently attached (tethered) to the therapeutic agents, biomolecules and biologics.

Composites of media and carriers (e.g. sintered together), and combinations of carriers can convey drugs and biologics and can control elution profiles.

Other exemplary dopants include barium titanate, zeolites (aluminosilicates), including siliceous zeolite and zeolites containing at least one component selected from phosphorous, silica, alumina, zirconia, calcium carbonate, biocompatible glass, calcium phosphate glass. The dopant can also be a growth factor consisting of epidermal growth factors, transforming growth factor α, transforming growth factor β, vaccinia growth factors, fibroblast growth factors, insulin-like growth factors, platelet derived growth factors, cartilage derived growth factors, interlukin-2, nerve cell growth factors, hemopoietic cell growth factors, lymphocyte growth factors, bone morphogenic proteins, osteogenic factors or chondrogenic factors.

In one embodiment, the dopant is hydroxyapatite deposited on a titanium surface. Both HA and TiO₂ constitute excellent biocompatible biointerfaces, both being biostable and safe in the body. Both can be termed bioreactive in that they can induce specific responses in certain tissues particularly bone tissue. The surface resulting from the deposition of HA on titanium as delivered by the micro-blasting technique combines the benefits of both materials. The TiO₂ is not fully covered by the dopant (HA) and therefore still presents to the biological tissue, while the HA affixed on and in the surface is not denatured by the deposition process and therefore conveys its full benefit to the surrounding tissue. In this manner the different benefits of both biomaterials can brought to bear in the biointerface and when further combined with the surface texture/morphology best suited to intended functionality of the implant, and moreover the availability of a drug delivery mechanism, can provide various methods for tailoring the therapeutic, compositional and morphological profile available to the patient end user.

In one embodiment, the dopant is a therapeutic agent. The therapeutic agent can be delivered as a particle itself, or immobilized inside or on a carrier material. In another embodiment, the therapeutic agent is immobilized with the carrier material as a homogeneous solid composition. Exemplary carrier materials include any of the other dopants listed herein (those dopants that are not a therapeutic agent) such as polymers, calcium phosphate, titanium dioxide, silica, biopolymers, biocompatible glasses, zeolite, demineralized bone, de-proteinated bone, allograft bone, and composite combinations thereof.

Exemplary classes of therapeutic agents include anti-cancer drugs, anti-inflammatory drugs, immunosuppressants, an antibiotic, heparin, a functional protein, a regulatory protein, structural proteins, oligo-peptides, antigenic peptides, nucleic acids, immunogens, and combinations thereof.

In one embodiment, the dopant is a radio opaque material, such as those chosen from alkalis earth metals, transition metals, rare earth metals, and oxides, sulphates, phosphates, polymers and combinations thereof.

In one embodiment, the carrier material is a biopolymer selected from polysaccharides, gelatin, collagen, alginate, hyaluronic acid, alginic acid, carrageenan, chondroitin, pectin, chitosan, and derivatives, blends and copolymers thereof.

In one embodiment, the dopant is delivered in a gaseous carrier fluid, such as nitrogen, hydrogen, argon, helium, air, ethylene oxide, and combinations thereof. In another embodiment, the dopant is delivered in a liquid carrier fluid. In one embodiment, the liquid is also an etching liquid (basic or acidic) In one embodiment, the dopant is delivered in an inert environment.

Another embodiment relates to the chemical treatment of metal surfaces for the purposes of adhesion. Good adhesion of paints and polymeric coatings to metal surfaces is an area of increasing technical importance. This technology can be used to pre-treat a surface by impregnating it with compounds having desired chemical functionality. These include but are not limited to polymers or silica materials having siloxane groups.

The pretreatment can be used to lay down a very strongly bound layer of seed polymer material on the surface. Further polymer coatings could then be attached to this seed layer rather than trying to attaching it directly to the surface of the metal.

The dopant is not limited to one compound but could be any combination of any of the materials listed or even any material(s) that do(es) not have the necessary mechanical properties to impregnate the surface if delivered singularly at high velocity to the surface.

In one embodiment, the dopant can be any material so long as it is passive, i.e., unreactive with the surface. It simply has to be at the surface when the oxide layer is breeched by the abrasive so that the oxide reforms around it.

In one embodiment, the dopant is nanocrystalline.

In one embodiment, the dopant is nanocrystalline hydroxyapatite.

In one embodiment the abrasive has a suitable property chosen from at least one of size, shape, hardness, and density to break the oxide layer. In one embodiment, the abrasive has a modus hardness ranging from 0.1 to 10, such as a modus hardness (Mohs) ranging from 1 to 10, or a modus hardness ranging from 5 to 10. In another embodiment, the abrasive has a particle size ranging from 0.1 μm to 10000 μm, such as a particle size ranging from 1 μm to 5000 μm, or a particle size ranging from 10 μm to 1000 μm.

Abrasive materials to be used in this invention include but are not limited to shot or grit made from silica, alumina, zirconia, barium titanate, calcium titanate, sodium titanate, titanium oxide, glass, biocompatible glass, diamond, silicon carbide, calcium phosphate, calcium carbonate, metallic powders, carbon fiber composites, polymeric composites, titanium, stainless steel, hardened steel, carbon steel chromium alloys, apatite grit (e.g., MCD grit, Himed, N.Y.), and combinations thereof.

The pressure of the fluid jet will also be a factor in determining the impact energy of the abrasive. The abrasive and dopant(s) do not have to be delivered to the surface through the same jet. They could be in any number of separate jets as long as they deliver the solid components to the surface at the substantially the same time, e.g., prior to reformation of the oxide layer if the surface is a metal. This allows a large amount of flexibility in optimizing the invention towards a specific need. In one embodiment, the fluid jet is selected from wet blasters, abrasive water jet peening machines, and wet shot peening machines. In one embodiment, the at least one fluid jet operates at a pressure ranging from 0.5 to 100 bar, such as a pressure ranging from 1 to 30 bar, or a pressure ranging from 1 to 10 bar.

In another embodiment, the at least one fluid jet is selected from dry shot peening machines, dry blasters, wheel abraders, grit blasters), sand blasters(s), and micro-blasters. In one embodiment, the at least one fluid jet operates at a pressure ranging from 0.5 to 100 bar, such as a pressure ranging from 1 to 30 bar, or a pressure ranging from 3 to 10 bar.

In other embodiments, blasting equipment can be used in conjunction with controlled motion such as CNC or robotic control. The blasting can be performed in an inert environment.

In one embodiment, the article is an implantable medical device. Exemplary medical devices include catheters, guide wires, and baskets used in the removal of pathological calcifications. In the case of biomedical devices it is desirable that the level of impregnation of the abrasive itself in the surface is minimal. The abrasive should further be biocompatible as it is likely that some impregnation will occur.

In one embodiment, the article is a metal, such as those metals chosen from pure metals, metal alloys, intermetals comprising single or multiple phases, intermetals comprising amorphous phases, intermetals comprising single crystal phases, and intermetals comprising polycrystalline phases. Exemplary metals include titanium, titanium alloys (e.g., NiTi or nitinol), ferrous alloys, stainless steel and stainless steel alloys, carbon steel, carbon steel alloys, aluminum, aluminum alloys, nickel, nickel alloys, nickel titanium alloys, tantalum, tantalum alloys, niobium, niobium alloys, chromium, chromium alloys, cobalt, cobalt alloys, precious metals, and precious metal alloys. In one embodiment, the metal is titanium.

In one embodiment the abrasive material is alumina (10 Mesh) while the dopant is HA with a particle size range of 0.1 to 3 μm. The mixed media is achieved by mixing the dopant and abrasive between the ratio of 5:95 and 95:5 HA to Silica volume % but more preferably between the ratio of 80:20 to 20:80 and most preferably in the ratio range 60:40 to 40:60. The silica bead has a Mohs hardness in the range of 0.1 to 10 but most preferably in the range of 2 to 10 and most preferably in the range 5 to 10. This mixed media is delivered to a titanium surface using a standard grit blasting machine operating in the pressure range of 0.5 Bar to 20 Bar, such as a pressure range of 2 to 10 bar, or a pressure range of 4 Bar to 6 Bar. The distance between the nozzle and the surface can be in the range of 0.1 mm to 100 mm, such as a range of 0.1 mm to 50 mm, or a range of 0.1 mm to 20 mm. The angle of the nozzle to the surface can range from 10 degrees to 90 degrees, such as a range of 30 degrees to 90 degrees, or a range of 70 to 90 degrees.

In another embodiment the abrasive material is silica (10 Mesh) while the dopant is HA with a particle size range of 0.1 to 3 μm. The mixed media is achieved by mixing the dopant and abrasive between the ratio of 5:95 and 95:5 HA to alumina weight % but more preferably between the ratio of 80:20 to 20:80 and most preferably in the ratio range 60:40 to 40:60. The Alumina grit has a Mohs hardness in the range of 0.1 to 10, such as a range of 2 to 10, or a range of 5 to 10. This mixed media can be delivered to a titanium surface using a standard grit blasting machine operating in the pressure range 0.5 Bar to 20 Bar, such as a pressure range of 2 to 10 bar, a range of 4 Bar to 6 Bat. The distance between the nozzle and the surface can range from 0.1 mm to 100 mm, such as a range of 0.1 mm to 50 mm, or a range of 0.1 mm to 20 mm. The angle of the nozzle to the surface can range from 10 degrees to 90 degrees, such as a range of 30 degrees to 90 degrees, or a range of 70 to 90 degrees.

One of ordinary skill in the art can appreciate the influence of machine parameters including jet velocity, operating pressure, venturi configuration, angle of incidence and surface to nozzle distances on the extent of impregnation of the dopant in the surface using these mixed media.

One of ordinary skill in the art can appreciate the effect of the size, shape, density and hardness of the abrasive material used on the extent of impregnation of the dopant in the surface using these mixed media.

One of ordinary skill in the art can appreciate the effect of the fluid stream itself, the blasting equipment using a gas medium (typically air) the effects of using inert gases as a carrier fluid e.g. N2 or noble gases such as Ar and He on the extent of impregnation of the dopant in the surface using these mixed media.

In the case of wet blasting equipment using a liquid as a carrier fluid (normally water), One of ordinary skill in the art can appreciate the effect of acidity and basicity on the extent of impregnation of the dopant in the surface using these mixed media.

As disclosed herein, the disclosed methods can be useful for modifying the surfaces of medical devices. In the context of medical device applications, dopants can be active (eliciting a biological response) or passive (not eliciting a biological response). Passive dopants can be conveyed to enhance lubricity or render a substrate radio-opaque, of enhance wear characteristics or enhance adhesion of an ad-layer, etc. Active agents can evoke a response from the host tissue in vivo, enhancing the functionality of the device or the surgery, or delivering a benefit as a secondary function to the device.

EXAMPLES Example 1

This Example describes the modification of titanium substrates by delivering hydroxyapatite as the dopant in one particle stream and alumina bead as the abrasive in a separate particle stream using a twin nozzle (“twin blasting”). Table 1 summarizes the pre and post blasting methods.

TABLE 1 The experimental program to blast substrates using various pre-blast and post-blasting combinations. Experiment # Pre Blast Post Blast PH01 Twin blasting Al₂O₃ PH02 Twin blasting Hydroxyapatite PH03 Twin blasting Twin blasting PH04 Hydroxyapatite Twin blasting PH05 Al₂O₃ Twin blasting PH06 Hydroxyapatite Al₂O₃ PH07 Twin blasting 2 x n/a speed

Experimental runs depositing various combinations of Al₂O₃ and HA either with twin blasting or separately, were carried out with a maximum of two blast passes—a per blast pass and a post blast pass—on each experimental group. The powder materials were stored in powder feeder hoppers, which formed part of a Comco Accuflo Micro-blaster system. One hopper for each system and at any one time two systems could be operated simultaneously. Each micro-blaster system fed into a separate nozzle housed in a Comco Advanced Lathe. Two nozzles were mounted on an adjustable blast head configured to synchronize the flow from each nozzle to the same point on the coupon's surface.

100 micron particle size Alumina bead—Alox, (Mohs hardness 9,) was used in all test runs where twin blasting (HA and Al₂O₃) or Al₂O₃ were run. The synthetic Hydroxyapatite (lot #: 260-07205, Manufacturer: SAI, France) used had a particle size range of 25 to 60 microns and was used in all test runs where twin blasting (HA and Al₂O₃) or HA were run.

In short both Accuflo micro-blasters are operating when the twin blasting process is run and one or the other is turned off when running the Al₂O₃ blast process (HA off) or the HA blast process (Al₂O₃ off).

Five 15 mm square Grade 5 titanium coupons (Titanium 6AL-4V Sheet Medical to ASTM F136 Spec) were treated for each test. The surface of each was fully covered with in a raster fashion first with the pre-blast treatment and then with the post-blast treatment at a feed rate of 3.175 mmsec-1.

The blasting parameters were not varied, except to change the blast head traverse speed for the final test.

The parameters were set as follows:

HA blast pressure: 60 PSI;

Alox blast pressure: 60 PSI;

HA nozzle ID: 0.030 inch;

Alox nozzle ID: 0.030 inch;

HA nozzle angle to surface: 80 degrees

Alox nozzle angle to surface: 80 degrees

Nozzle distance from surface: 0.5 inch

Following blasting, the coupons were subjected to a cleaning treatment involving 20 minutes ultrasonic washing in isopropyl alcohol to remove any material that was not intimately affixed to the surface. After the ultrasonic cleaning the coupons were rinsed with deionized water and air-dried in an oven at 40° C. for one hour.

Samples were submitted for XPS (X-Ray photoelectron spectroscopy); FTIR (Fourier Transform Infrared Spectroscopy); Surface Roughness analysis—Stylus Profilometry; to determine the relative concentration of Ca, P, and Ti at the surface of each sample in conjunction with the morphological characteristics of each sample. Results for XPS analysis and stylus profilometry are shown in Table 2.

TABLE 2 The XPS and Stylus Profilometry results of the Ti substrates processed using various pre-blast and post-blast combinations. Sample Mean Mean Mean Mean SD Sample No: Description Ca/P % HA % Ti % Al Ra (nm) Ra (nm) PH01 1^(st) twin blasting 1.8 5.4 4.66 9.30 549.67 35.91 2^(nd) Al₂0₃ only PH02 1^(st) twin blasting 1.71 22.58 0.0 0 379.67 37.88 2^(nd) HA only PH03 1^(st) twin blasting 1.73 19.52 1.54 0 437.17 72.85 2^(nd) twin blasting PH04 1^(st) Ha only 1.77 18.36 2.1 0 526.17 34.00 2^(nd) twin blasting PH05 1^(st) Al₂0₃ 1.79 17.27 1.74 2.10 494.17 23.34 2^(nd) twin blasting PH06 1^(st) Ha only 1.88 4.78 5.35 9.38 599.33 71.55 2^(nd) Al₂O₃ only PH07 Twin blasting 1.75 20.12 1.32 0 495.50 37.54 2 x speed

The data indicates that varying the pre-blast and post-blast conditions as outlined in the experiment results in variation in the % HA retaining on the surface, the introduction but also in differences in the quantity and coverage of Hydroxyapatite on the surface. Minimal variation in the Ca:P ratio occurs.

In the table it can be seen that when Al₂O₃ is used as a separate blasting medium, some of it gets impregnated into the surface of the Ti substrate. This can be seen in experimental runs PH01, PH05 and PH06. The converse is also true—when Al2O3 is not used as a separate medium but combined with the twin blasting process, none of the Al2O3 particles get impregnated into the Ti, and this can be seen in the remaining samples, which are elaborated below. It should be noted that the PH01 and PH06 groups demonstrate the highest roughness values of all the groups, indicating that the post-blast with Al2O3 further roughens a surface blasted with the twin blasting process and giving rise to a dopant (HA) deposition.

This fact alone demonstrates that by varying the nature of back to back micro-blasting operations, it is possible to either incorporate or prevent the deposition of Al2O3 onto the Titanium substrate. This implies that there is not a need to acid etch the Ti after the treatment (to remove any Al2O3 particles impregnated in the surface), as is the normal practice.

In sample PH02, pre-blasted with the twin blasting process and post-blasted with the deposition of HA on its own, the % HA retained on the surface is 22.5%, with respect to the other elements, while displaying the least roughness of all the experimental groups, indicating that the HA is filling up the troughs on the surface created by the blasting processes. This is further exemplified by the fact that there is no surface presence of Titanium, as it is completely masked by the HA blanket layer.

In sample PH03, pre-blasted and post-blasted with the twin blasting process, in essence double blasting the substrate. This revealed a similar % HA retained on the surface, i.e., 19.5%, with a Titanium presence of 1.54%. The roughness is lower that other twin blasting post-blasted groups (PH04 and PH05), indicating a double filling of the troughs with HA in the Ti roughened surface but not in the same manner as in PH03 where the HA blanket covers all the Titanium substrate.

In sample PH04, the HA was deposited in the pre-blast step followed then by the twin blasting process. It is known from previous experimental work that the initial coating of HA is loosely adherent on the substrate. The post-blast twin blasting process further pummels this HA into the surface in conjunction with depositing HA of its own. In either case 18.6% HA is manifest on the surface, being consistent with previous twin blasting only trials.

In group PH05, Al2O3 is deposited in the pre-blast step followed then by the twin blasting process. There is a resultant manifestation of 2.1 Aluminium on the surface from the Al2O3 only pre-blast step, indicating that Al2O3 will anchor itself in Titanium based substrates. All other aspects of this surface are as one expects with the twin blasting process, i.e. Ti %, HA % Ca:P ratio, surface roughness.

Group PH06 has a similar result to that of group PH01 and this is because they both share a Al2O3 post-blast stet. Both groups show high Aluminum % b retained on the surface and both have high roughness values. The average Ti % and HA % on the surface is the same for both indicating that irrespective of how the initial step of placing HA on the surface is conducted, the post-blasting with a abrasive-blast step only results in a burying of the HA deep in the surface layer and high abrasive retention, while fresh Titanium is churned up to the surface giving rise to an increase in its manifestation over what would be expected.

Increasing the speed of the blast head traverse over the titanium coupon has not had a detrimental effect on the levels of HA deposited by the twin blasting only one step process. One would have expected a less rough surface with less HA deposited and a higher showing of Titanium on the surface. If anything there is a slight improvement in the level of HA deposited on and in the surface. This indicates that the twin blasting process for depositing HA on a Titanium substrate is very robust and allow for a doubling of the process speed with a consequent halving of the HA quantity required to achieve the same surface result.

Example 2

A mixer (block) of FIG. 10 was used to deposit a dopant, namely hydroxyapatite (HA), in the presence of an abrasive (Al₂O₃) onto Grade V titanium.

The hydroxyapatite powder (from SAI, France) was loaded into a power feeder unit (hopper) associated with a Comco Standard Lathe. The abrasive (100 micron alumina, from Comco Inc, CA) was loaded into a second powder feeder. Both powder feeders were operating at a pressure of 90 psi and were connected to a mixer device which consisted of a with two inlets and a single outlet which ensured the two powder flows were blended together. The output of the mixer was connected to a single microblast nozzle inside the Comco Lathe. The output of this nozzle was used to blast a 15 mm×15 mm CP titanium coupon (Titanium Sheet Grade 5 Medical). The nozzle to surface distance was 20 mm and the nozzle was held at 90° to the surface. The silicon carbide nozzle had an orifice of 3.8 mm long by 1 mm wide and traversed the surface at 1 cm per sec.

After blasting, the treated titanium samples were subjected to an air blasting process operating at 120 psi to remove any material that was not intimately affixed to the surface. Samples were ultrasonically cleaned in iso-propyl alcohol for 5 minutes. The sample was rinsed and then ultrasonically washed in isopropyl alcohol for a further five minutes. Samples were then dried in air and analysed using SEM-EDX to determine the relative concentration of elements present at the surface of each coupon. This analysis revealed a surface with 7.9% Ca, 5.7% P, 14.9% Ti and a large amount of C and O. The high levels of Ca, P, C and O is consistent with the deposition of a hydroxyapatite layer on the surface of the titanium coupon.

Example 3

This Example describes a coaxial nozzle design of FIG. 7. The coaxial nozzle included a first gas stream in the centre of the device and second gas stream coaxially surrounding the first stream. This allowed a gas flow to carry a first stream of particles down the centre of the coaxial device. A second gas stream flows outside of this and surrounds the first gas stream and can transport a second set of particles. The second gas stream was arbitrarily set at an incident angle of 14 degrees to the vertical. This ensured that the second gas stream could converge with the first gas stream, thereby focusing both sets of particles on to a single zone on a substrate.

This coaxial nozzle was mounted on a Comco Standard Lathe micro-blasting station and this was used to deposit a series of hydroxyapatite (HA) coatings on to a titanium substrate (Grade V Ti coupons, 15×15×1 mm dimensions). The substrates were cleaned prior to coating by immersing in ultrasonically agitated IPA for five minutes. Hydroxyapatite (SAI, France) was used as the dopant and either MCD grit (Himed, N.Y.) or 100 um alumina (Comco, Calif.) was used as an abrasive.

The coaxial nozzle was maintained 20 mm above the substrate and moved at a speed of 13 mm/sec along the surface of the substrates. The centre flow of particles was directed into a microblast nozzle with 1.2 mm diameter outlet. The second outer flow of particles was directed through a circular orifice with an opening of 200 microns. All powders were flowed at a pressure of 90 psi.

The following coatings were deposited:

Sample 1: MCD was flowed through the first central opening and HA was supplied through the second outer coaxial opening. This deposited a coating onto the surface of the titanium. SEM-EDX analysis determined that the HA level (Ca+P) was 16% (atomic weight %).

Sample 2: The HA flow was turned off and the test was repeated with only the MCD grit flowing through the centre. This produced a HA level of 12%, due to the presence of microblasted apatite MCD grit on the surface.

Sample 3. Alumina was introduced through the first central channel and HA was again allowed to flow through the outer coaxial channel. This produced a coating with 14% HA. 

1. An apparatus for abrasively blasting a substrate, comprising: at least two hoppers for receiving at least two sets of particles including a first set of particles comprising an abrasive and a second set of particles comprising a dopant; a mixer for receiving and mixing the at least two sets of particles from the at least two hoppers to form a particulate mixture; and at least one fluid jet for delivering the at least two sets of particles to the mixer, or the particulate mixture to the substrate, the at least one fluid jet being positioned downstream of the at least two hoppers.
 2. The apparatus of claim 1, wherein the at least one fluid jet is positioned at the base of the at least two hoppers.
 3. The apparatus of claim 1, wherein the at least one fluid jet is positioned at the base of the mixer.
 4. The apparatus of claim 1, further comprising delivery tubes connecting each of the at least two hoppers to the mixer.
 5. The apparatus of claim 1, wherein each delivery tube is linear and has an incident angle with respect to the vertical.
 6. The apparatus of claim 5, wherein the delivery tube for the first set of particles has an incident angle normal to the vertical and the delivery tube for the second set of particles comprising the dopant is delivered at an incident angle parallel to the vertical.
 7. The apparatus of claim 1, further comprising a second fluid jet for delivering the second set of particles to the mixer.
 8. An apparatus for abrasively blasting a substrate, comprising: a first particle stream comprising an abrasive and a second particle stream comprising a dopant; a conical or frustoconical mixer comprising at least two channels penetrating through the mixer, wherein the respective particle streams enter the channels separately and exit the mixer to impact the substrate as a particulate mixture of the first and second particle streams; and at least one fluid jet to deliver at least one of the first and second particle streams to the mixer, or to deliver the particulate mixture to the substrate.
 9. The apparatus of claim 8, wherein the two or more channels are linear.
 10. The apparatus of claim 9, wherein the block has a longitudinal axis and each of the two or more channels has an incident angle relative to the longitudinal axis ranging from 0° to an angle formed by the outer conical surface of the block, the incident angle of each of the channels being the same or different.
 11. The apparatus of claim 8, wherein the at least one fluid jet is positioned upstream of the mixer to deliver at least one of the first and second particle streams to the mixer.
 12. The apparatus of claim 8, wherein the at least one fluid jet is positioned between the mixer and the substrate to deliver the particulate mixture to the substrate.
 13. The apparatus of claim 8, wherein the two ore more channels merge into a single channel within the block.
 14. An apparatus for abrasively blasting a substrate, comprising: a coaxial nozzle for delivering a first set of particles comprising at least one dopant and a second set of particles comprising an abrasive, wherein an inner tubing of the nozzle delivers a particle stream comprising a first set of particles, and an outer tubing delivers a pressurized gas comprising the second set of particles that encircles and converges inwardly toward the first set of particles to mix and homogenize the first and second set of particles, and wherein a resulting mixture of the first and second particles bombard and impregnate and/or coat the substrate with the at least one dopant.
 15. The apparatus of claim 14, wherein the nozzle is a fluid jet.
 16. A method of modifying a substrate, comprising: delivering substantially simultaneously a first set of particles comprising a dopant and a second set of particles comprising an abrasive from at least one fluid jet to a surface of the substrate to impregnate the substrate with the dopant, each nozzle having an incident angle to the vertical ranging from 0° to 85°; and moving the substrate in a direction parallel to the substrate surface during the delivering to deposit a track of the dopant on the substrate surface.
 17. A method of modifying a substrate, comprising: delivering substantially simultaneously a first set of particles comprising a dopant and a second set of particles comprising an abrasive from at least one fluid jet to the substrate to impregnate the substrate with the dopant, wherein the first and second set of particles overlap at an area between the at least one fluid jet and the substrate, and wherein a cross section of the overlap area has a substantially homogeneous distribution of the first set of particles. 18-57. (canceled) 